1. Field of the Invention
The invention pertains to a video system that compresses video data for transmission or storage and decompresses the video data for display. More particularly, the invention pertains to a video system and a method for intracoding video data.
2. Description of the Related Art
Video systems transmit, process and store large quantities of video data. To create a video presentation, such as a video movie, a rendering video system displays the video data as a plurality of digital images, also referred to as xe2x80x9cframes,xe2x80x9d thereby simulating movement. In order to achieve a video presentation with an acceptable video quality, or to enable transmission and storage at all, a conventional video system modifies the video data prior to transmission or storage. For instance, the video system compresses and encodes the video data to reduce the bit rate for storage and transmission.
In a conventional video system a video encoder is used to compress and encode the video data and a video decoder is used to decompress and to decode the video data. The video encoder outputs video data that has a reduced bit rate and a reduced redundancy. That is, the technique of video compression removes spatial redundancy within a video frame or temporal redundancy between consecutive video frames.
The video encoder and video decoder may be configured to apply one of two types of coding to compress the video stream, namely intracoding and interceding. These two types of coding are based on the statistical properties of the video frames. When the video frames are coded using intracoding, the compression is based on information contained in a single frame (the frame that is compressed) by using the spatial redundancy within the frame. Intracoding, thus, does not depend on any other frames. In contrast, interceding uses at least one other frame as a reference and codes a difference between the frame to be compressed and the reference frame. Intercoding is thus based on a temporal redundancy between consecutive frames in the video data.
The field of video compression is subject to international standards, e.g., International Telecommunications Union (ITU) standard H.263 that defines uniform requirements for video coding and decoding. In addition, manufacturers of video coders and decoders modify or build upon the international standards and implement proprietary techniques for video compression.
Despite the existence of the international standards and the proprietary techniques, there is still a need for improved techniques for video compression. For example, as the quality of a displayed video movie depends directly from the technique used for video compression, any improvement of the video compression technique makes the video movie more pleasing for the viewer.
An aspect of the invention involves a method of coding a stream of video data including a stream of video frames. The method divides each video frame into a matrix of a plurality of subblocks, wherein each subblock includes a plurality of pixels. The method further defines nine prediction modes, wherein each prediction mode determines a mode according to which a present subblock is to be coded. The method further selects one of the nine prediction modes to encode the present subblock. The selected prediction mode provides for a minimum error value in the present subblock.
Another aspect of the invention involves a video system for coding and decoding a stream of video data that includes a stream of video frames. The video system includes a video encoder and a mode selector. The video encoder is configured to receive a stream of video data including a stream of video frames and to divide each video frame into a matrix of a plurality of subblocks, wherein each subblock includes a plurality of pixels. The mode selector is in communication with the video encoder and is configured to define nine prediction modes. Each prediction mode determines a mode according to which a present subblock is to be coded. The mode selector is further configured to select one of the nine prediction modes to encode the present subblock, wherein the selected prediction mode provides for a minimum error value in the present subblock.
Once the video system has selected the best prediction mode to encode the pixels of the present subblock, the video system encodes the minimum error value and transmits the encoded minimum error value within a compressed bitstream to the decoder. The minimum error value represents a difference between predicted pixels of the present subblock and the original pixels of the subblock. The decoder uses the predicted pixels and the difference to the original pixels to accurately reconstruct the video frame.